Wenckebach, Karel Frederik (1864-1940), Dutch internist. Wenckebach held professorships in internal medicine at Groningen, Netherlands, at Strasbourg, and at Vienna. His areas of research included embryological problems and the pathology of heart diseases and the circulation of the blood. In 1914 he published classic descriptions of various forms of cardiac arrhythmia. He was the first to demonstrate the value of quinine in the treatment of paroxysmal fibrillation. In 1928 he established a mechanical theory of cardiac pain in coronary occlusion.